The present invention relates to a steering return control apparatus and method of an MDPS (Motor Driven Power Steering), and more particularly, to a steering return control apparatus and method of an MDPS, which can correct a target position value for return control by monitoring a neutral drive state of a vehicle in real time, and return a steering wheel to a position at which the vehicle can be driven in the neutral state, even though wheel alignment is distorted or an error occurs in a steering angle sensor, thereby preventing a degradation of return control performance.
In general, a motor driven power steering (MDPS) refers to a system that provides an assist torque in a steering direction of a driver, using an electric motor, and thus enables the driver to easily handle a steering wheel.
Unlike an existing hydraulic power steering (HPS), the MDPS can automatically control an operation of the electric motor depending on a driving condition of a vehicle, and thus improve steering performance and steering feel.
At this time, the MDPS includes a torque sensor and a vehicle speed sensor, in order to determine the driving condition of the vehicle. The torque sensor measures a steering torque of the driver, inputted to the steering wheel, and the vehicle speed sensor measures a vehicle speed.
The driver applies a steering input to turn the vehicle, and then releases the steering wheel when determining that the vehicle was turned to a desired extent. However, the steering wheel is returned to the center through a returning operation.
The returning operation of the steering wheel is performed through a self alignment torque of a tire. Typically, when the vehicle is being turned at a velocity of 5 km/h to 30 km/h, the returning operation can be usefully used.
However, the self alignment torque applied to the steering wheel is not enough to return the steering wheel to the center because a residual steering angle remains due to a frictional force of the steering system.
Thus, a function of assisting the returning operation is inevitably provided in order to completely return the steering wheel to the center.
Therefore, the MDPS applies a return torque which is calculated based on the steering wheel, and assists the returning operation of the steering wheel, thereby improving the returning performance.
The related art is disclosed in Korean Publication Patent No. 2010-0114995 published on Oct. 27, 2010 and entitled “Steering return method of MDPS”.
When the MDPS calculates the return torque based on the steering angle and returns the steering wheel, wheel alignment may be distorted by the load of the vehicle or a road condition and left and right friction charge of a mechanical part, an error may occur in the initial zero adjustment of a steering angle sensor, or a hysteresis and offset of the steering angle sensor may occur. In this case, the return control may not be optimized.